1. Field of the Invention
The present invention relates to a dry-sump lubrication type four-stroke cycle engine suitable for a vehicle, such as a straddle type all-terrain four-wheel vehicle or a motorcycle, and, more specifically to improvements in oil pumps.
2. Description of the Related Art
A generally known dry-sump lubrication type four-stroke cycle engine is provided with two pumps, i.e., an oil feed pump and a scavenging pump. The oil feed pump pumps up oil from an oil tank or an oil reservoir chamber and feeds the oil to parts needing lubrication by pressure. The scavenging pump returns the oil lubricated and dripped from the lubricated parts into the oil tank or the oil reservoir chamber.
FIG. 21 shows an oil pump mechanism included in a dry-sump lubrication type four-stroke cycle engine disclosed in JP-A No. 288214/1994. The oil pump mechanism is provided with two pumps, i.e., a scavenging pump 300 and an oil feed pump 305. The scavenging pump 300 and the oil feed pump 305 are arranged coaxially and the respective rotor shafts 310 and 311 of the pumps 300 and 305 are connected by a shaft coupling mechanism 313 to arrange the pumps 300 and 305 compactly. The scavenging pump 300 has a pump housing 301 formed in a clutch cover 302. The oil feed pump 305 has a housing 306 attached to a crankcase 307. The respective rotor shafts 310 and 311 of the pumps 300 and 305 are formed separately, are supported on the pump housings 301 and 306, respectively, and are connected by the shaft coupling mechanism 313.
In the above-mentioned conventional structure, the respective rotor shafts 310 and 311 of the pumps 300 and 305 are formed separately and connected by the shaft coupling mechanism 313, the pump housing 301 of the scavenging pump 300 is mounted on the clutch cover 302, and the pump housing 306 of the oil feed pump 305 is mounted on the crankcase 307. Therefore, a large space is necessary for the pumps 300 and 305, many parts are necessary, and much time is necessary for assembling the pumps 300 and 305 and for processing the crankcase 307 and the clutch cover 302.
Accordingly, it is an object of the present invention to provide a dry-sump lubrication type four-stroke cycle engine provided with a compact, simple oil pump mechanism.
According to one aspect of the present invention, a dry-sump lubrication type four-stroke cycle engine comprises: an oil feed pump configured to feed oil by pressure to parts needing lubrication, the oil feed pump having a rotor; a scavenging pump configured to return oil lubricated the parts needing lubrication into an oil tank, the scavenging pump having a rotor; a crankcase configured to contain a crankshaft; and a clutch cover configured to cover a side of the crankcase so as to form a clutch chamber which contains a clutch of the engine, wherein the rotor of the oil feed pump and the rotor of the scavenging pump are fixedly mounted on a single rotor shaft, and wherein the oil feed pump and the scavenging pump are mounted on the clutch cover.
Since the respective rotors of the oil feed pump and the scavenging pump are fixedly mounted on the common rotor shaft, and the oil feed pump and the scavenging pump are mounted on the clutch cover, the oil feed pump and the scavenging pump are formed from a small number of component parts, machining work for manufacturing a shaft coupling mechanism for connecting shafts is not necessary, and the oil feed pump and the scavenging pump can be easily assembled. Since both the oil feed pump and the scavenging pump are mounted on the clutch cover, the crankcase can be easily processed, and a lower part of a clutch chamber accommodating the clutch can be effectively utilized and hence the dry-sump lubrication type four-stroke cycle engine can be formed in compact construction. Usually, a filter for filtering the oil fed by the oil feed pump is supported on the clutch cover. Therefore, an oil passage between the oil feed pump and the filter can be simply formed in the clutch cover when the oil feed pump is mounted on the clutch cover.
Preferably, the dry-sump lubrication type four-stroke cycle engine further comprises a pump gear fixedly mounted on the rotor shaft; and a crankshaft gear mounted on the crankshaft and meshed with a clutch gear mounted on the clutch, wherein the pump gear is meshed with the crankshaft gear.
Since the crankshaft gear serves for both driving the clutch and the pumps, which reduces parts necessary for forming a power transmission mechanism.
Preferably, a discharge part and a suction part of the oil feed pump is connected through a relief valve, and oil discharged from the discharge part through the relief valve is returned to the suction part of the oil feed pump.
Since the oil discharged by the oil feed pump through the relief valve is returned directly to the suction part of the oil feed pump instead of returning the same into an oil tank, only a short relief passage needs to be formed in the clutch cover, which simplifies the construction. Since the oil discharged from the oil feed pump can be directly sucked by the oil feed pump, the oil released through the relief valve can be efficiently used.
Preferably, the relief valve is built in a pump housing of the scavenging pump.
In this structure, the number of parts necessary for forming the relief valve and space for disposing the relief valve can be reduced.
Preferably, the oil feed pump and the scavenging pump are disposed in a space located in a lower part of a space behind the crankshaft and in front of the clutch.
Thus, the space covered by the clutch cover can be effectively used for installing the oil feed pump and the scavenging pump.
Preferably, the clutch chamber is formed so as to be able to contain the oil up to a predetermined oil level in a lower portion of the clutch chamber. The rotor shaft may be positioned below the predetermined oil level so as to be immersed in the oil contained in the clutch chamber.
Thus, the oil feed pump is able to pump the oil without causing air inclusion at the start of pumping even after the dry-sump lubrication type four-stroke cycle engine has been kept stopped for a long time.
Preferably, a pump housing and a pump cover of the scavenging pump are fastened in that order to an inner surface of the clutch cover. A rotor chamber for containing the rotor of the oil feed pump is formed in the clutch cover, the rotor chamber having one open side, the open side of the rotor chamber being covered with the pump housing. A rotor chamber for containing the rotor of the scavenging pump is formed in the pump housing, the rotor chamber having one open side, the open side of the rotor chamber being covered with the pump cover. The rotor shaft is supported on the pump cover and the pump housing.
In this structure, the oil feed pump and the scavenging pump need a small number of parts, can be simply assembled and has simple construction.